Where are symbols placed in ELF sections based on their type?

Question

Accepted Answer

Functions go to .text; initialized globals to .data (or .bss if their value is zero); uninitialized globals to .bss (or legacy COMMON); externals stay undefined.

Symbol Type
COMMON Section?
ELF Section
Condition

Functions
-
.text
Always

Initialized globals
No (default/-fno-common)
.data
value != 0

Initialized globals
No
.bss
value == 0

Uninitialized globals
Yes (-fcommon, GCC <10)
COMMON
Tentative definition

External
-
UNDEFINED
Defined elsewhere

Local symbols:

Appear only in relocatable object files
Stripped from executable and shared object files
static variables go to .data or .bss based on initialization

COMMON section:

Historical feature for uninitialized global variables
Final linkage not known at compile time
Disabled by default since GCC 10 (-fno-common)

Go deeper:

Weak symbol (Wikipedia) — why uninitialized globals behave as "weak"/COMMON, and what -fno-common changes.

Symbol Type	COMMON Section?	ELF Section	Condition
Functions	-	.text	Always
Initialized globals	No (default/-fno-common)	.data	value != 0
Initialized globals	No	.bss	value == 0
Uninitialized globals	Yes (-fcommon, GCC <10)	COMMON	Tentative definition
External	-	UNDEFINED	Defined elsewhere